This invention relates to a compact circuit package having an improved construction for clamping to an external object to enhance heat transfer from the compact circuit package.
Heat conducting, electrically insulating substrates have been advantageously employed to retain heat generating electrical components along a first substrate side while a second oppositely disposed substrate side may be mounted to a heat sink to permit the heat generated by the electrical component to pass through the electrically insulating substrate to be dissipated at the external heat sink. One desirable construction is shown in the U.S. Pat. No. 3,958,075 entitled "High Power Thick Film Circuit With Overlapping Lead Frame", which issued on May 18, 1976 to Lance R. Kaufman.
A wide variety of circuit constructions may be located at or near the insulating substrate to be within a cavity provided by the surrounding insulating housing. By way of example, an electrical power converting thyristor firing circuit could be used, such as disclosed in U.S. Pat. No. 4,257,091 entitled "Electrical Power Converter Thyristor Firing Circuit Having Noise Immunity", which issued on Mar. 17, 1981 to Lance R. Kaufman. Optically couplable circuit elements could be used, such as shown in the U.S. Pat. No. 4,156,148 entitled "Photocoupling Structure For a Solid State Power Control Device", which issued on May 22, 1979 to Lance R. Kaufman or as shown in U.S. Pat. No. 4,266,140 entitled "Positioning Means For Optically Couplable Circuit Elements", which issued on May 5, 1981 to Lance R. Kaufman. One or more terminals could be used for the main input and/or output power connections such as disclosed in U.S. Pat. No. 4,215,235 entitled "Lead Frame Terminal", which issued on July 29, 1980 to Lance R. Kaufman. One or more variable resistance devices could be used such as disclosed in U.S. Pat. No. 4,250,481 entitled "Variable Resistance Device For Thick Film Circuitry", which issued on May 10, 1981 to Lance R. Kaufman. One or more dual resistor elements could be used such as disclosed in U.S. Pat. No. 4,196,411 entitled "Dual Resistor Element", which issued on Apr. 1, 1980 to Lance R. Kaufman. Many additional circuits could also be employed.
Heat conducting, electrically insulating substrates containing one or more heat generating electrical components have been advantageously connected to an insulating housing including a cavity surrounded by one or more edges or abutments which engage the substrate to limit the depth of entry of the substrate into the cavity. Such insulating housing provides an outer rim surrounding the cavity which is generally located in a plane spaced from another plane substantially containing the substrate second side. In such manner, clamping pressure may be applied to the insulating housing to clamp the substrate second side against an external heat dissipating object such as a heat sink to permit heat to pass from the substrate to the external heat sink without encountering any intervening thermal barriers such as solder, metalization, epoxy or the like. One highly desirable device employing peripheral clamping of the substrate by an insulating housing is shown in U.S. application Ser. No. 834,601 entitled "Power Switching Device Having Improved Heat Dissipation Means", which was filed on Sept. 19, 1977 by Lance R. Kaufman. Another highly desirable device employing peripheral clamping of the substrate by an insulating housing is shown in U.S. Pat. No. 4,218,724 entitled "Compact Circuit Package Having Improved Circuit Connectors", which issued on Aug. 19, 1980 to Lance R. Kaufman.
To provide a high degree of heat transfer, it is desirable to maintain an intimate engagement between substantial portions of the substrate second side and a corresponding area of surfaces of the heat sink. In some instances, electrically insulating and heat conducting substrates, such as ceramic for example, are punched or stamped from larger uncured sheets and thereafter fired or cured at extremely high temperatures, i.e. approximately 5000.degree. F., which may cause deviations or warping along the substrate second side. For example, warping may cause a surface to deviate between spaced planes by one-one hundredth of an inch per each linear inch. Where such warping becomes excessive, it is difficult to clamp the substrate to the heat sink to provide the desired substantial intimate engagement between the facing surfaces without subjecting the substrate second side to additional expensive and time consuming processing such as grinding and lapping for example.